Treatment of alloys containing iron group metals



TREATMENT OF ALLOYS CONTAINING IRON GROUP METALS Stephen M. .Shelton, Albany, '0reg., assignor to Oregon Metallurgical'Corporation, Albany, reg., a corporatior'rof Oregon 'Nb num. Filed Nov. 24, 1958, See. No. 775,705 Claims. (Cl. 75-97) This invention relates to the recovery of metalsfrom alloys, and more particularly to a method of producing solutions of metalsalts as ,a-step inthe recovery of these metals from alloys containing the same. The invention concerns, specifically, metals of the iron group, i.e. nickel, cobalt, etc. which have been used extensively in the production of alloys of a special nature.

Exemplary of the alloys to which this. invention relates, are the cobalt and/or nickel containing refractory type alloys and corrosion resistant alloys which have been developed in recent'years. These may have cobalt and/ or nickel concentrations ranging up to about 80% or more.. With scrap containing more than about nickel or cobalt, recovery of the nickel or cobalt fractions is practicable from a commercial standpoint, provided the recoveryican be done in an economical manner.

Characteristically, these alloys have been prepared to have a maximum amountof resistance toflcorrosion, oxidization, and chemical .attack.. The alloys also maybe quite tough and relatively'hard to disintegrate. It is these veryproperties which distinguish the alloys and make them useful as astructural material, which have made'diflicult the manufacture of compounds therefrom. Thus these alloys have resisted dissolution inJacids, causticj solution, salt baths, and other conventional hydrometallurgical recovery techniques." In" generaltterms ltlrisiinvention contemplates as the first ste'p; in producing metal salts from such alloys the production ran intermediate fprocessin g alloy by. melting 'tog'ethera mirrture of (the alloy w from which' rnetal is ofishttm i am c d and r u a d amo ts-Pf, aluminuni Through'fthe-. introduction of aluminum, an intern w 191 win q fi erect 21 W ar ed; Whi e t original alloy" n rayjhave .been tough, difiicult to, disintegrate, and chemically resistant," the intermediate l fprocessing{ alloy is characterized generally by being (1') readi'ly 'dis'int genesis parade form usinglmilling grjinding, 6r btlir conventional pulverizing' techniques, {and i (2) markedly rnore reactive chemically with the murmur firming, dis's'olv-ing acids. -Thus the processinga'lloy may be ground to 'cornrniriuted torm and the metal c6nstituents-;thereof -r' ed uce'd to kcorripounds of dissolving acids," usingt'ar less compl'err equipment than previously necessary using knownrecoverymethods and with'considerablerapidity.v

The;advantages;of the process outlined include con siderable savingsin timerfaster use oilprocessing e uip-I ment, and ajieduction in .the, extent and complexity of-the equipment required, greater ease in handling and proc caste a nieree zss in .a. 1 1. aprimarypbjectaofrthis nvenr 1 pm? In thou icnis u l' fr m a l ys. bil l l slhelsf r .o flfi s rmin an t mledia 'e ject of the invention to provide such a method which comprises melting with the initial alloy aluminum to pro maybe treated according to the' method of this duce a "processing alloy which is friable and chemically the pulverant product to acid solvation.

The invention is described hereinbelow in conjunction reactive, pulverizing this processing alloy and subjecting wth certain specific examples, which are not intendedto constitute; the limits of the invention, but which are included for illustrative purposes.

Illustrative of the nickel and/orcobalt-containing al-' loys which may be processed according to this invention; are the alloys Waspaloy (an alloy containing about 19.5% chromium, 57.0% nickel, 13.5% cobalt, 4.3%

mo1ybdenum,.3.1% titanium,.l.3% aluminum, 1.2% iron,

and traces of carbon), Udimet 500 (an alloy containing about 19% chromium, 19% cobalt, 4.0% molybdenum, 3.0% titanium, 3.0% aluminurn,-0.1% carbon, and the balance nickel),"and Discaloy an alloy containing about 13.5% chromium, 26.0% nickel, 54.0% ir0n,3.0% mo lybdenum, 1.6% titanium, 0.8% manganese, and traces of carbon). These aforementioned alloys are typical of high temperature, high stress alloys finding use today in special'applications, and as can be seen from the corn positions given, .contain substantialxamounts of metals from the irongroup. Corrosion-resistant alloys which invention are illustrated by, such alloys as Monel metal (a nickeltures of two or more metals wherein one of the metals copper alloy), Chromel (a nickel-chromium alloy), and

cobalt-copper alloys. fWhile various materials have been listed, the invention is not limited to use with these particular materials, but in general may beapplied to mixis ametal fromjthe iron group, While alloys containing relatively small percentages ofnickeland cobalt-may be processed as contemplated by this invention, as a practical matter usually such processing is not justified from an economicstandpoint unless the percent; ge of nickel and cobalt in'jthe alloyis more than about 10%."

.In practicing theinvention, generallyoptimum results were obtain ed when sufficient aluminum was incorporated with the original alloy to produce an aluminum concen tration in the-intermediate processing alloy of about 20% or' more. A' 20% aluminum concentration produced alloys which were friable, and had chemical 're-' activities witlrth e usual solvent acids, such as sulfuric or hydrochloric, which were from 10fto IOO times or moregreater-than prior to the addition of aluminum. Greater amounts of aluminum'm ay be employed foriri stance, aluminum concentrations in the processing alloy of or'more maybe used, but ordinarily noadvantage in friab'ility'or reactivity is incurred through such uSeQa nd the addition of large amounts of aluminum there ifo'r'rn ieiely has'the eifectof adding to thejcost of processin'g. Satisfactory results were obtained with aluminum concentrations" in the range of 13-15 %,]but with concen trationsmuch below this, the character of the' original alloy isnot'changed sufficiently to produce a useful im provement in the ease of processing. This is'notto say;

however, that the addition of small amounts of; 'alurr'rin'uiri' ordinarilyjby heating a mixture of the alloy'frorn which salts'a're to be derived anda" requisite amount of ammo num. In" some instances, especially when chips and/or turnings are being processed, it inay be desirable to bri quette a mixture ofthe metals prior'to melting. This procedure may be'particularly-advantageous if are or 'induc tion melting is performed'under vacuum. After amelt has been prepared and the'metal constituents have mixed with each other, the mass is cooled, with the production of a metal ingot partially comprised of aluminum. Dur

in'g" cooling, 'it'is' not'u'ncomm'on for the ingot tooracle 2,946,677, Y Patented July reduced to a comminuted form prior to reaction. with acid, as this increases the surface area of the metal available for contact with acid and thus the reaction rate of the alloy with acid. Disintegration of the alloy may be done in any of a number of conventional units, such as the usual ball or hammer mill, pneumatic attrition mill, and the like.

After disintegration, the comminuted alloy product is reacted with acid, with the production of metal salts of the acid and the evolution of hydrogen. In general, these acids comprise the usual metal oxidizing acids used in hydrometallurgical recovery processes. The acids generally are water soluble (i.e., more than about 80%), have a relatively high ionization potential, and are substantially stable and resistant to decomposition at atmospheric boiling temperatures. The concentration of acid used will vary, depending upon the metal sought to be dissolved, the solubility of the metal salts, etc. Illustrative of the acids which may be employed in the metal salt formation are the inorganic or mineral acids such as sulfuric, hydrochloric, nitric, and hydrofluoric acids. From an economic standpoint, since sulphuric acid is readily available commercially, this acid lends itself to the practice of this invention.

The amount of acid used in reaction with the powdered alloy normally will vary from stoichiometric amounts to amounts in excess of this. Since aluminum stands above the metals of the iron group (iron, cobalt, and nickel) in the electromotive series, it is necessary to have suflicient acid completely to combine with the aluminum before expecting the formation of salts of the iron-group metals.

During reaction of the powdered alloy with acid, the temperature of the reaction mixture ordinarily is raised above room temperature, as this also has the effect of speeding up the acid reaction. Thus temperatures of from between 80 C. and 100 C. may be used if the reaction is carried out at atmospheric pressure. -Room temperatures may be employed, however, with satisfactory results. So also may temperatures above 100 C. be used if the reaction is carried out at elevated pressures. Superatrnospheric pressures, other than allowing higher temperatures, apparently have little effect on the rate of reaction of the alloy with acid.

Other means may be employed to hasten the reaction of the powdered alloy with acid, such as providing agitation for the reaction mixture, removing spent or partially spent acid, etc. Such procedures would be apparent to one skilled in the art.

As an example of the process of this invention, a melt was prepared by heating to the melting pointa mixture of 100 parts of a high cobalt, refractory alloy containing 62% cobalt, 27% chromium, 6% molydenum, 2% nickel and 3% of a mixture of iron, manganese, silicon, and carbon (with each of the latter components not exceeding 1%) and 25 parts of aluminum. (Unless otherwise indicated, parts and percentages used herein refer to parts and percentage on a weight basis.) Scrap turnings of the alloy were used, and these were briquettedwith chips of aluminum using 25 tons pressure prior to producing the melt. The melt was made in an electric arc furnace, under vacuum. The melt was cooled to room temperature, with the approximately 20% aluminum alloy ingot which was formed cracking during cooling into coarse pieces of approximately walnut size.

The aluminum alloy was very friable and easily crushed with a mortar and pestle into a powder which passed through a 20 mesh Tyler screen. Fifteen parts of this powder was placed in a reaction vessel, and reacted with 200 parts of a 50% aqueous sulfuric acid solution. The sulfuric acid was poured slowly over the alloy powder, and the alloy powder and acid solution mixture simmered 4 for about of an hour. At the end of this time, the alloy powder was completely dissolved.

A similar sample of alloy powder was reacted with an excess (600 parts) of sulfuric acid, using a similar procedure, with substantially complete dissolving of the powder. An excess of hydrochloric, nitric, and hydrofluoric acids (25% solutions in water) was also effective substantially to completely dissolve such alloy powder.

In another example, a melt of about 100 parts of the refractory alloy having the composition set forth above and about .17 parts of aluminum was prepared, to yield an aluminum alloy having an aluminum content of about 14.5%. This alloy was tougher than the aluminum alloy first prepared, and not as friable, although the alloy could be ground to powder form.

Fifteen parts of the alloy containing 14.5% aluminum, ground to a powder which passed through a 20 mesh Tyler screen, was reacted with 200 parts of 50% aqueous sulfuric acid, over a period of about two hours, while simmering the reaction mixture. At the end of this time interval, the powdered alloy had been substantially completely dissolved.

An aluminum alloy prepared from 100 parts of the refractory alloy having the composition set forth above and about 100 parts of aluminum was very friable and easily ground to powdered form. This alloy and the 20% aluminum alloy were about equally reactive with 50% aqueous sulfuric acid and hydrochloric acid solutions.

In another treatment, 100 parts of Monel metal (67% nickel, 28% copper, 1-2% manganese, and 1.9-2.5% iron) was alloyed with 25 parts of aluminum. An extremely friable aluminum alloy was formed, which was readily ground to comminuted form. Fifteen parts of the ground-up alloy was simmered with 200 parts of 50% aqueous sulfuric acid over a period of about one hour. At the end of this time, the alloy powder had been substantially all dissolved. Similar results were obtained with 50% hydrochloric acid solution.

A sample of 100 parts of Waspaloy was alloyed with 25 parts of aluminum. The result was a friable product readily ground to powdered form. A 15 part sample of this product was reacted with 200 parts of 50% aqueous sulfuric acid, over a period of about two hours and at a temperature of from 100 C. At the end of the twohour period, substantially all the powder had dissolved.

In another treatment, parts of an alloy composed of about 0.3% carbon, 1.1% manganese, 0.6% silicon, 19.0% chromium, 9.0% nickel, 1.2% molybdenum, 1.2% tungsten, 0.4% columbium, 0.3% titanium, and the remainder iron was alloyed with 20 parts of aluminum. A friable product resulted, and a 15 part sample of the product ground to a powder reacted readily with 200 parts 50% aqueous sulfuric acid, with dissolving of the sample.

Thus, to summarize the invention, a process is contemplated whereby alloys may be readily changed to a state which makes them susceptible to chemical breakdown, i.e., reaction with acid materials whereby salts of the metallic constituents of the alloys are formed. Increased chemical reactivity is produced in an alloy coniointly with a change in the physical characteristics of the alloy which results in turning the alloy into a material which is considerably more amenable to mechanical disintegration. The process thus has particular importance in connection with the recovery of iron-group metals, such as cobalt and nickel, from alloys which'normally resist physical and chemical degradation.

It is claimed and desired to secure by Letters Patent: 1. In the recovery of iron-group metals from a starting alloy containing the same, the process of producing salts of the iron-group metals in the starting alloy by alloying the starting alloy with aluminum to produce a friable aluminum alloy product, and dissolving the aluminum alloy product in an oxidizing acid which is reactive 5 with the product to produce salts of the acid and irongroup metals.

2. In the recovery of iron-group metals from a starting alloy containing the same, the process of producing salts of the iron-group metals in the starting alloy by alloying the starting alloy with aluminum thus to produce a friable aluminum alloy product, mechanically breaking up the aluminum-alloy product to form a particulate mass, and reacting the particulate mass with an oxidizing acid which is reactive with the mass to produce salts of the acid and iron-group metals.

3. In the recovery of iron-group metals from a starting alloy containing the same, the steps of rendering the starting alloy amenable to acid reaction through ('1) alloying the starting alloy with aluminum to produce a friable aluminum alloy product, and (2) mechanically disintegrating the aluminum alloy product so formed and reacting the disintegrated aluminum alloy product with an oxidizing acid which is reactive with the product to produce salts of the acid and iron-group metals.

4. In the hydrometallurgical recovery of iron-group metals from an alloy containing the same, the process of forming a processing alloy from the original alloy by melting into the original alloy suflicient aluminum to produce an aluminum alloy product containing morethan about 15% aluminum, mechanically disintegrating the aluminum alloy product, and reacting the disintegrated product with mineral acids which are reactive with the aluminum alloy to produce salts of the acid and irongroup metals.

5. In the hydrometallurgical recovery of metals selected from the group consisting of nickel and cobalt from an alloy containing the same, the process of alloying the original alloy with aluminum to produce a friable processing alloy which contains more than about 15 aluminum, mechanically disintegrating the processing alloy to obtain a pulverant product, and reacting the pulverant product with a mineral acid selected from the group consisting of sulfuric, hydrochloric, nitric, and hydrofluoric acids and mixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS McMaster Aug. 26, 1952 

1. IN THE RECOVERY OF IRON-GROUP METALS FROM THE STARTING ALLOY CONTAINING THE SAME, THE PROCESS OF PRODUCING SALTS OF THE IRON-GROUP METALS IN THE STARTING ALLOY BY ALLOYING THE STARTING ALLOW WITH ALLUMINUM TO PRODUCE A FRIABLE ALUMINUM ALLOY PRODUCT, AND DISSOLVING THE ALUMINUM ALLOY PRODUCT IN AN OXIDIZING ACID WHICH IS REACTIVE WITH THE PRODUCT TO PRODUCE SALTS OF THE ACID AND IRONGROUP METALS. 